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Thread: high base fog

  1. #1
    rmolson's Avatar
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    high base fog

    Base density level


    Getting back into photography after a two year absence. I have been getting overly heavy negatives on my 35mm work So I ran a whole zone test Using HP5 rated at 250 in Claytons F-76 1:9 I got a base fog of .28!!! Which put my zone I at .50 .28 =.22. Obviously why off. I checked on both of my densitometers and they agreed. The calibration strip was spot on,.I use to do this for a living. The House is not air conditioned and the temperature got up in the 80s this summer How resistant to heat fog is HP 5? Claytons F-76 is suppose to be similar to D-76 and I never got base fog this high with D76 on Tri X.

  2. #2
    cliveh's Avatar
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    This may be over development.

    “The contemplation of things as they are, without error or confusion, without substitution or imposture, is in itself a nobler thing than a whole harvest of invention”

    Francis Bacon

  3. #3
    selmslie's Avatar
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    Try a fresh roll of HP5 and fresh developer. Heat and other factors may have fogged your film.

  4. #4

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    I haven't tested HP5+ in particular, but with FP4+, Delta 100 and Pan F+ I normally get a film base+fog reading of ~0.30, which is normal for me with Ilford films. I get lower film base+fog levels with films like Kodak TMX/TMY (around 0.20). Ilford films simply have a higher base density. No problem.

    Your zone I on the other hand seems high, although be rating the film at 250 you're giving nearly an extra stop. Hard to diagnose however without more detail regarding your film speed/testing process.

  5. #5

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    I've completed my testing of Ilford HP5+ 4x5 sheet in HC-110, varying dilution/time as needed to achieve N+2 through N-5. All tests were done by contact in camera, using a 31-step tablet, with fresh film & developer. I found the fb+f density to vary from .12 to .31 (averaging, fwiw, around .18). There were no definite trends to give clues as to why it varied randomly. However the plots of all resulting NET densities v. exposure made complete sense. Probably the most difficult variable to contend with is lens flare or bellows flare, If you're copying a step wedge that's illuminated by a lightbox, make sure you mask the step wedge carefully.

  6. #6
    Bill Burk's Avatar
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    4x5 films tend to be manufactured on "clear" base, while 35mm films may have a "base tint" for antihalation purposes.

    rmolson, have you ruled out what you see isn't just normal base tint?

  7. #7
    rmolson's Avatar
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    IF .30 is normal base density for HP5 then my reading make sense. Just use to much lower base density from sheet and roll film. Will need to adjust development times though.



 

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